Answer:
b. Maintaining robust Chinese exports and a favorable balance of trade for China.
Step-by-step explanation:
China is a country that has giant export benefit because they are able to produce goods and services cheaper than most other countries, to capitalize on this advantage they keep exchange rates lower so that their exports are cheaper and they have a competitive advantage of lower prices in the world market. Keeping the currency undervalued allows China to keep their exports cheaper and thus take advantage of a favorable balance of trade.
Hope that helps.